1. Field
The following description relates to a semiconductor device. The following description also a semiconductor device used in an electric device or a high voltage device.
2. Description of Related Art
In understanding the functionality of an electric device or a high voltage device, there are two important features, which are a breakdown voltage blocking current flow in an off state and resistance that pertains when current flows at a switched-on state. These two features show appropriate trends because of use in a relevant silicon material. In other words, when breakdown voltage is high in a high voltage electric device, a drift region is low doped so Rsp, which is Specific on-resistance, resistance generally becomes high. By contrast, when the drift region is heavily doped, resistance becomes low and a corresponding breakdown voltage is also greatly lowered.
Moreover, Reduced Surface Field, hereinafter referred to as ‘RESURF’, technology is to be used on a drift region to obtain high breakdown voltage. A depletion region is extended to an entire n-type epitaxial layer by growing a thick n-type epitaxial layer on a p-type substrate. Accordingly, a strength of an electric field vertically applied on a substrate is greatly reduced. As a strength of an electric field is reduced, a corresponding breakdown voltage is greatly increased by overcoming limitations of a depletion region that is restricted to an original side distance. An accumulation region is formed on a drift region positioned below a gate insulator layer and there is a problem that arises when the length of the accumulation region extends a gate charge Qg value between regions of a gate and a drain or a gate and a source or a gate and a corresponding bulk increases. As a result, then there is a problem that a Figure of Merit, hereinafter referred to as ‘FOM’, Ron×Qg, which is considered important in characterizing the performance of a high voltage device or electric device greatly increases.
Therefore it is advantageous to optimize resistance of a drift region through which current flows to reduce conduction loss.